Lactose Intolerance
Lactose intolerance is when an organism is unable to digest lactose properly or possibly at all. Lactose is a sugar that is found in milk as well as milk products. People who suffer from lactose intolerance enzymatically differ from lactose tolerant people by the fact that the enzyme lactase is inefficient or decreased. Lactase is the enzyme that would digest the lactose. The majority of humans become lactose intolerant after weaning. However, some human populations have shown a mutation causing them to continue to be lactose tolerant into adulthood. Symptoms *Abdominal pain or bloating *Nausea *Diarrhea *Vomiting These symptoms occur when someone injests a large quantity of lactose without being able to digest it with lactase. The lactose then sits in the digestive system and acts as food for the bacteria, then causing the symptoms to occur. Lactase Lactase in an enzyme in the B-galactosidase group, that is produced in the walls of the small intestine. Lactase is the enzyme that is suppose to break down the lactose sugar in milk into glucose and galactose. These are smaller sugars which then get absorbed into the bloodstream (national digestive diseases). Most humans are born with lactase because milk is necessary for children, but shortly after weaning the majority of the human population begins to experience down-regulation in the transcription of lactase. This then causes lower or no expression of lactase in the small intestine, which leads to lactose intolerance in adults. Lactase is encoded by the gene LCT. Lactase Persistance Many people are able to continually digest lactose into adulthood. This persistence is why some adults are still able to drink milk and injest milk products without any of the symptoms of lactose intolerance. While lactose intolerance is known to be recessively and autosomally-inherited, lactase persistance acts as a dominant trait. Lactase expression, whether presistance or non-persistance, have been able to be linked with two SNPs. These SNPs are located upstream from the LCT gene in the MCM6 gene. The MCM6 gene isn't involved with the lactase enzyme exactly, it overlaps with the enhancer of the LTC gene. Lactase persistance seems to be present when cysteine-13910 nucleotide mutates into thymine-13910, and when''' guanine-22018 mutates into adenosine-22018. Lactase non-persistance, leading to lactose intolerance, seems to be present when the sequence contains c'ysteine-13910 and guanine-22018. ' Studies have proven that the genotypes of LCT that have cytesine and thymine nucleotides(LCT-13910CT) as well as LCT that have two thymine nucleotides (LCT-13910 TT) are associated with the lactose persistant phenotype. This proves that the having only one thymine, which is a lactase persistant allele, acts as a dominant affect.'' (6) '' Another study shows that the LTC-13910T site acts as an enhancer region for the LTC gene. ''(6)''' This could be the greatest reason why having a thymine versus a cysteine in this position up-regulates lactase persistance. When reviewing an analysis of ones own genome, for example on 23andme.com, it may give you your genotype as either GG, GA, or AA. Knowing what these genotypes actually mean and what the difference is will help a lot when comparing this data. LCT-G is known as an allele for lactose intolerance, while LCT- A is known as a single allele for lactase persistance. LCT-A is a dominant allele in this case because even when the genotype is LCT-GA, the organism would be lactase persistant (baring any environmental causes). With the genotype LCT-GG the individual would be lactase non-persistant, and be lactose intolerant. With the genotypes LCT-GA, and LCT-AA the individual would be lactase persistant. Environmental causes could also affect lactose intolerance. The ability of lactase to digest lactose into glucose and galactose could depend on the different bacteria that is present in the gut. It's possible to have the same genotype as another individual, yet have different results. This could be because of an environmental factor, or possibly something in the genes that hasn't been discovered yet. References * "Lactase Persistence." ''Wikipedia. Wikimedia Foundation, 09 May 2013. Web. . * "Lactase." Wikipedia. Wikimedia Foundation, 17 Sept. 2013. Web. . * "Lactose Intolerance." 23andme. N.p., n.d. Web. . * "Lactose Intolerance." Wikipedia. Wikimedia Foundation, 09 Dec. 2013. Web. 17 Sept. 2013. . * "LCT." Genetics Home Reference. N.p., n.d. Web. . * Mattar, Rejane, Daniel Ferraz De Campos Mazo, and Flair José Carrilho. "Lactose Intolerance: Diagnosis, Genetic, and Clinical Factors." National Center for Biotechnology Information. U.S. National Library of Medicine, 05 July 2012. Web. .